1. Field
Embodiments relate to an electrophotographic image forming apparatus, and more particularly, to a polygonal rotating mirror, a light scanning unit employing the same to process a synchronization signal and compensate for an image, and an electrophotographic image forming apparatus employing the light scanning unit.
2. Description of the Related Art
An image forming apparatus, such as a laser printer, forms an image by scanning a light beam onto a photosensitive drum by using a light scanning device to form an electrostatic latent image, developing the electrostatic latent image into a toner image by using toner, and transferring the developed toner image onto a printing medium.
A light scanning device uses a polygonal rotating mirror including a plurality of reflective surfaces to scan a light beam onto a photosensitive drum. Light beams are continuously scanned as the polygonal rotating mirror rotates. In a single color image forming apparatus for producing a single color image, a light scanning device scans a light beam by using one polygonal mirror. In a color image forming apparatus for producing a color image, a light scanning device scans four light beams corresponding to the respective colors of black (K), cyan (C), magenta (M), and yellow (Y) by using one or more polygonal rotating mirrors. For example, the light scanning device may use a single polygonal rotating mirror to scan four light beams corresponding to four colors of black (K), cyan (C), magenta (M), and yellow (Y), two polygonal rotating mirrors to scan light beams corresponding to two colors, respectively, or four polygonal rotating mirrors to scan light beams of a single color, respectively.
In order for a light scanning device to scan a light beam onto a photosensitive drum with a correct timing, a synchronization signal detection unit for detecting a horizontal synchronization signal of a scanned light beam is required.
A conventional synchronization signal detection unit detects a horizontal synchronization signal by using beam detecting sensors. The detected horizontal synchronization signal is then transferred to a printer video controller (PVC). The PVC transmits video data to a laser diode driver (LDD) in a light scanning device according to the received horizontal synchronization signal, and the LDD controls on/off operation of a light source according to the video data so as to emit a light beam.